The present invention relates to gas generators and, more particularly, to a pyrotechnic gas generator containing stored gas for inflating an inflatable vehicle occupant restraint device, such as an air bag.
It is known to use gas generator systems incorporating a stored gas (or “hybrid”) inflator to inflate an inflatable vehicle occupant restraint, such as an air bag, to restrain and protect a vehicle occupant in the event of a collision. Typically, such inflators include a container defining a first chamber for storing an inflation gas under high pressure. The container also has an opening through which inflation fluid may flow to inflate the protection device. A first rupturable closure extends across the opening in the container to block fluid flow through the opening. A second chamber is formed either inside the container, or in a manner so as to enable fluid communication between the second chamber and the first chamber. The second chamber contains a quantity of gas generant material. A passage is provided which allows fluid communication between the first and second chambers. A second rupturable closure blocks the passage to restrict fluid communication between the first and second chambers. Upon receiving a signal from a crash sensor algorithm, the gas generant in the second chamber is ignited, producing combustion products which increase pressure in the second chamber to a predetermined level. This causes the second closure to rupture, thereby opening the passage and allowing the combustion products to flow into the first chamber, affecting heating of the inflation fluid stored in the first chamber. This increases pressure in the first chamber, producing rupture of the first closure and allowing the inflation fluid to inflate an inflatable element (for example, an air bag) of the vehicle occupant protection system.
Several concerns exist with the conventional hybrid inflator design described above. The sequence of events, namely ignition of the gas generant, increased pressure in the second chamber, rupture of the second closure to open the passage, propagation of combustion products to the first chamber, heating of the inflation fluid stored in the first chamber, increase of inflation fluid pressure, and rupture of the first closure that are required to inflate the air bag causes unnecessary delay in air bag inflation. In addition, the first and second chambers are typically not in fluid communication unless the gas generant has been ignited, rupturing the second closure. Thus, the gas generant is not exposed to the high pressures produced by the inflation gas stored in the first chamber. Accordingly, the pyrotechnic gas generant chamber must generally be pressurized prior to achieving sustained combustion of the gas generant therein. This typically involves the use of a booster composition that is first ignited by an associated igniter thereby elevating the pressure within the gas generant chamber and thus facilitating sustained combustion of the pyrotechnic gas generant. Another disadvantage with the conventional hybrid inflator design described above is the need for two separate high pressure chambers, one chamber typically housing a pyrotechnic gas generant and the other chamber housing pressurized gas. A design of this type increases the manufacturing complexity and cost of the inflator.